This invention relates to a thin film solar cell or a thin film semiconductor device.
Recently, the development of thin film semiconductor devices employing amorphous, microcrystalline, or polycrystalline semiconductors as well as amorphous silicon (hereinafter denoted by a-Si) has been vigorously carried out to overcome the deficiencies of semiconductor devices using conventional single crystals. It has been known that the non-crystalline, microcrystalline and polycrystalline semiconductor devices have properties such that the distribution of current in a horizontal direction of a film is low since the resistivity of the film is high and that the resistivity is reduced if the film is crystallized by using electromagnetic or thermal means.
An example of an a-Si solar cell will be first described as a thin film semiconductor device which has been conventionally employed.
FIG. 1 shows a cross-sectional view of a conventional p-i-n junction-type amorphous solar cell 2 formed on a stainless steel (conductive) substrate 1. FIG. 1(a) is a case wherein an electrical terminal 5 is provided on a lower portion of the conductive substrate 1 opposite an electrode 4 of a cell area covered with a transparent conductive film 3. FIG. 1(b) illustrates a structure wherein another electrode 6 is formed on an upper surface (cell area) of the substrate 1 by removing a part of the semiconductor thin film (amorphous silicon junction layer) on the substrate 1 by physical or chemical means. The structure shown in FIG. 1(a) has a disadvantage because locations for providing the semiconductor device and associated wiring are remarkably limited. The structure shown in FIG. 1(b) has a disadvantage because the a-Si layer is etched away or the deposited region of an a-Si layer must be previously restricted, thus complicating the manufacturing process or greatly reducing the cell area.